Lee C. W. E., Sui C. H. S., Izumo Takeshi. (2025). The evolutions of single-year and multiyear El Niño from preconditioning to decay stages : direct wind-driven versus boundary-reflected oceanic responses. Journal of Climate, 38 (5), p. 1205-1220. ISSN 0894-8755.
Titre du document
The evolutions of single-year and multiyear El Niño from preconditioning to decay stages : direct wind-driven versus boundary-reflected oceanic responses
Journal of Climate, 2025,
38 (5), p. 1205-1220 ISSN 0894-8755
Advancing our understanding of single-year and multiyear El Niño events is essential for a better forecast of El Niños and assessment of their global socioeconomic impacts. Here, we compare these two types of El Niños in reanalysis and coupled model data. We further develop an approach in a linear continuously stratified ocean model to quantifying direct wind-driven (DWD) and boundary-reflected (BR) responses to wind stress forcing from the reanalysis and coupled model datasets. For single-year El Niños, the positive North Pacific meridional mode charges additional heat content to the tropical Pacific through DWD processes in year21 before the development year (year0), leading to the earlier event development. The subsequent discharge and zonal-advective reflective feedbacks by BR processes also start earlier and are intensified by wind anomalies of a more eastward fetch. Finally, during the mature boreal winter and decay spring in year1, the equatorial western Pacific winds turn into easterlies, terminating DWD downwelling Kelvin waves and the positive feedback. In contrast, multiyear El Niños feature a lower preconditioning recharge state in year21, later development and less eastward-extending wind and sea surface temperature anomalies in year0, and weaker delayed negative feedbacks and persistent western Pacific westerly winds in year1. The resultant insufficient BR negative feedbacks and lasting DWD downwelling Kelvin waves allow El Niño to continue into year1/year2. The approach developed here and the results that show the fundamental dynamic processes regulating El Niño's duration should help in improving El Niño-Southern Oscillation (ENSO) seasonal forecasting. SIGNIFICANCE STATEMENT: El Niño events have global climate impacts, but their duration from single- to multiyear is a challenging prediction problem. Here, we investigate the mechanisms determining their duration. We analyze their evolutions and quantify wind-forced ocean responses. We show that the early establishment of tropical Pacific warm water volume, the eastward shift of wind stresses, and the center of warm sea surface temperature influence the strength and timing of the following negative feedbacks that modulate an event's decay. The El Niño's spatial and temporal diversities are linked by dynamical processes. The above mechanisms can be applied to observation monitoring, model, and forecast diagnosis. It could potentially help in mitigating the global socioeconomic and environmental impacts of ENSO.
Plan de classement
Sciences du milieu [021]
;
Limnologie physique / Océanographie physique [032]
